The semiconductor integrated circuit (IC) industry has experienced rapid growth. In the course of the IC evolution, functional density (defined as the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. A scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. But, such scaling down has increased the complexity of processing and manufacturing ICs. For these advances to be realized, similar developments in IC manufacturing are needed.
To further improve a performance of a semiconductor device, a work function of a metal gate stack of the semiconductor device may be adjusted. In some instances, the adjustment is performed by depositing several work function metal layers having different materials and/or removing a portion of the work function metal layers.